Polyunsaturated fatty acids (PUFAs) are not synthesized in a human body, thus it is necessary to consume them as a food instead. It has been known for a prolonged time that PUFAs, as a component for cell serum membrane, are an important biological component that is inevitably required in a brain, especially, of an infant.
In 1970's, Eskimos in Greenland were observed, and as a result, it was found that there is a relationship between a low rate of heart disease and a great amount of consumption of long-chain ω-3 PUFAs [see Dyerberg, L. et al., Amer. J. Clin Nutr. 28:958-966 (1975); and Dyberg, J. et al., Lancet 2 (8081): 117-119 (Jul. 15, 1978)]. More recent researches confirmed the effects of heart-related protection [see Shinkkawa, H. World Rev Nutr Diet, 88: 100-108 (2001); and von schacky, C., and Dyerberg, J., World Rev Nutr Diet, 88: 90-99 (2001)]. Moreover, it was found that several diseases react to the treatment using ω-3 fatty acids, for example, restenosis to some extent after angioplasty, flammatory or rheumatoid arthritis, asthma, psoriasis, and eczema. It was found that γ-linolenic acid (GLA; ω-6 PUFA) reduces blood pressure elevation related to stress and improves its performances on the arithmetic test. It was found that GLA and dihomo-γlinolenic acid (DGLA, another ω-6 PUFA) inhibits platelet aggregation, induces vasodilation, reduces the level of cholesterol, and inhibits proliferation of blood vessel wall smooth muscles and fibrous tissues [see Brenner et al., Adv. Exp. Med. Biol. 83:85-101 (1976)]. It was found that administration of GLA or DGLA alone or in combination with eicosapentaenoic acid (EPA, ω-3 PUFA) reduces or prevents gastrointestinal bleeding, and reduces and prevents other side effects caused by non-steroidal anti-inflammatory drugs (U.S. Pat. No. 4,666,701). In addition, it has been found that GLA and DGLA prevents and treats endometriosis and premenstrual syndrome (U.S. Pat. No. 4,758,592) and treats myalgic encephalomyelitis and chronic fatigue after viral infection (U.S. Pat. No. 5,116,871). Other evidences indicate that PUFAs can participate in control of calcium metabolism. This suggests that PUFAs are useful for treating and preventing osteoporosis and renal or urinary calculus. Finally, PUFAs can be used in the treatment of cancers and diabetes [see U.S. Pat. No. 4,826,877 and Horrobin et al., Am. J. Clin, Nutr. 57 (Suppl.): 732S-737S (1993)].
In general, PUFAs are classified into ω-6 and ω-3 fatty acids derived by unsaturation and elongation of essential fatty acids such as linoleic acid (LA) and α-linolenic acid (ALA), respectively. Here, ω refers to a number of carbons counted from the end of a methyl group to a point of a first double bond in the fatty acid.
It is confirmed that various fatty acids such as ω-6 fatty acids including linoleic acid, dihomo-γ-linolenic acid and arachidonic acid, and ω-3 fatty acids including α-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid and docosapentaenoic acid exhibit each different physiological effects.
Such ω-6 and ω-3 fatty acids are inevitable for maintaining a good health, and they must be consumed in a ratio of about 4:1. However, a westernized diet nowadays has lead to a serious disparity of consuming ω-6 fatty acids on average 20 times more than ω-3 fatty acids. Therefore, in order to recover such a disparity, it is necessary to ingest ω-3 fatty acids.
Docosahexaenoic acid (hereinafter, referred to as ‘DHA’) is a ω-3 fatty acid having 22 carbon atoms and 6 double bonds. The efficacies of DHA have been known to have contribution to mainly reinforcing brain functions and visual developments. Such DHA is commonly used as a nutritional supplement, and a highly purified product of DHA can be used as a medicine for hyperlipemia.
Docosapentaenoic acid (hereinafter, referred to as ‘DPA) is a ω-3 fatty acid having 22 carbon atoms and 5 double bonds. DPA has been known to have effects on thrombosis inhibition, carbohydrate metabolism, and improvement in vascular endothelial cell plasticity.
Eicosapentaenoic acid (hereinafter, referred to as ‘EPA’) is a ω-3 fatty acid having 20 carbon atoms and 5 double bonds. EPA exerts various physiological activities such as inhibiting platelet aggregation in a human body, reducing a level of triglyceride in a blood plasma, reducing a level of very low density lipoproteins (VLDLs) and low density lipoproteins (LDLs), increasing a level of high density lipoproteins (HDLs), reducing a blood viscosity and blood pressure, and serving antiphlogistic and antineoplastic functions.
For examples relating to oil which uses such polyunsaturated fatty acids, Japanese Patent No. 2572692 discloses DHA triglyceride and its production, Japanese Patent No. 2602743 discloses EPA triglyceride and its production, and Japanese Patent Laid-Open Publication No. 2003-160794 discloses ω-3 type unsaturated fatty acid in triglyceride. Further, U.S. Pat. No. 6,852,758 discloses ω-3 type unsaturated fatty acid in diglyceride, U.S. Pat. No. 6,410,078 discloses triglycerides rich in polyunsaturated fatty acids, and U.S. Pat. No. 6,200,624 discloses triglycerides containing ω-6 fatty ester moieties that include ARA and DHA. Furthermore, EP patent No. 1544281 discloses DHA in monoglyceride, and WO 00/18944 discloses triglycerols of enriched CLA content.
Additionally, WO 2005/5144 suggests using an oil containing DPA for improving a state of lacking arachidonic acid and increasing arachidonic acid. However, the DPA content is extremely low, and the oil is derived from microorganisms with a high production cost. WO 2003/24237 discloses an oil composition comprising ω-3 fatty acids capable of preventing accumulation of body fat. However, the content of the ω-3 fatty acid among the constituent fatty acids of diglyceride is less than 15% by weight, which is low.
Many of these patents use ω-3 fatty acids, but the approaches were made on a wide range of fatty acids having 18 or more carbon atoms. Examples containing a great amount of polyunsaturated fatty acids were not to be found. Especially, the patents relate to mostly triglycerides containing polyunsaturated fatty acids, and most of the patents relating to diglycerides containing polyunsaturated fatty acids also had no application of DPA functionalities. Moreover, there have been no examples of limiting the content of EPA.
Meanwhile, important ω-3 fatty acids of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA) are found from each different type of fish or ocean plankton. They are also producible from microorganisms [e.g., porphyridium and mortierella]. However, there are disadvantages in that the cost is high, and the cultivation on a commercial scale is difficult.
For example, Japanese Patent Laid-Open No. 8-214891 discloses a production of an oil and fat containing highly polyunsaturated fatty acid in high concentration by reacting the oil and fat with a deformed immobilized-enzyme. Japanese Patent Laid-Open No. 6-287593 suggests a method for stabilizing fat or oil by transesterification to inhibit oxidation of polyunsaturated fatty acid contained in fish.
However, the above-mentioned patents contains the polyunsaturated fatty acid in a great amount of 45% by weight or more, thus concentration thereof is difficult and the production unit cost is not effective.